Effect

Generation I

Selfdestruct inflicts damage, and causes the user to faint. Though its power is listed as 130, the target's Defense will be halved during damage calculation (unless it is at a value of 1), effectively doubling the power to 260.

If Selfdestruct breaks a target's substitute, the user will not faint, though its image will be replaced by a blank image. Additionally, if the user of Selfdestruct had a substitute at the time of such a situation, uses Substitute later, or switches out, its regular image will once again become visible.

If the user of Selfdestruct attacks first and faints itself, the target will not attack or be subjected to recurrent damage during that round.

In Stadium, if Selfdestruct breaks a target's substitute, the user will faint. The base power listed in Stadium is the one after halving Defense, i.e. 260.

Generation II

Selfdestruct's power is increased to 200. The target's Defense is still halved, effectively doubling the power to 400.

In other games

Self-Destruct does not cause the user to faint, but instead cuts its HP in half, and affects all Pokémon, items, and walls within one tile of the user, reducing HP by half on teammates, by 50 on hostile Pokémon, and destroying all walls, items, and special tiles. Self-Destruct cannot be used in rain or on any floor with a Pokémon with the Ability Damp. Additionally, Fire-type Pokémon take only 50% of usual damage.